Sulfur poisoning in Ni-anode solid oxide fuel cells (SOFCs): Deactivation in single cells and a stack

The most thermodynamically stable sulfur compound in the anode electrode at SOFC temperature is H2S, which dissociates on a nickel (Ni) surface according to a chemisorption mechanism. In this study, SOFC performance losses have been quantified in the presence of H2S contamination. The deactivation process has been well quantified by correlating it to Ni surface coverage by sulfur through a Temkin-like isotherm adsorption process. The detailed microscopic features of an Ni-based electrode have been taken into account to quantitatively predict atomic sulfur adsorption on the Ni surface. The results show that, in anode-supported cells, the entire available Ni surface is affected by sulfur contamination and not just the three-phase-boundary (TPB) region. Experiments on both commercial single-cells and on a stack have been described in this work. The H2S concentration was varied from 0.8 to 6.5 ppm(v) in the single-cell experiments, and between 0.01 and 25 ppm(v) in the stack experiment. The time-to-coverage evaluation has been established on the basis of the relationship between the sulfur capacity of the Ni anode and the sulfur flow rate through the fuel feed.